Designed to alleviate heavy alpine traffic and combat rising CO2 emissions, more than 300 freight and passenger trains will whisk through the tunnel each day once it becomes fully operational in December.

Construction began on the monster project in 1999 and, over the following 17 years, engineers blasted through more than 70 types of rock and excavated 31 million tons of material to construct the tunnel.

Great day for Switzerland...opening of the new train tunnel #gottardo2016 ...longest train tunnel on earth! Great job💪🇨🇭 proud to be swiss!

The opening ceremony drew Italian Prime Minister Matteo Renzi, Swiss Federal President Johann Schneider-Ammann, French President Francois Hollande and German Chancellor Angela Merkel who sat together in a VIP carriage for the maiden voyage of the first train through the tunnel.